In reality, the Danube is anything but blue. The color of its waters, which typically range from gray to an impenetrably muddy brown, befit one of the world’s most heavily industrialized waterways.

The factories and power plants and other commercial activities that line the river’s banks have been largely unfettered by environmental restrictions, and have historically used it as a convenient sewer.

That has made much of the river a place you wouldn’t want to fall into, let alone drink.

The Danube’s high level of pollution and acidification has never been regarded as an asset, but that view may now have to be tempered.

Last Monday a vast pond holding highly alkaline toxic red sludge, a byproduct of an aluminum processing plant in Hungary, burst through its dike, sending a horrific flood into the surrounding countryside.

Within three days the flowing disaster, a spill rivaling the size of the blown-out BP oil well that recently ravaged the Gulf of Mexico, had found its way to the Danube. The predicted consequences were uniformly dire.

Alarmed governments downstream from the Hungarian plant responded by pouring large quantities of acidic gypsum and vinegar into the plumes of sludge. As swimming pool owners know, a proper mix of acid and alkali will result in a neutral - and largely harmless - balance.

Meanwhile, the mighty Danube has apparently risen to its own defense; its acidic waters have worked to help neutralize the invading alkali to an extent the scientists had not expected.

The Danube may never be blue, and the aphorism that two wrongs do not make a right is still valid, but this is a remarkable example of nature working things out for the best.

The serendipitous outcome provides a second chance, or at least buys time for those national neighbors who share the Danube.

We hope those countries turn this lesson into an opportunity to transform the languishing Danube from its slum status to its rightful place as one of the world’s truly splendid great rivers.